To provide a thermosetting resin composition having a benzoxazine ring, which has a reduced coefficient of linear thermal expansion and excellent dimensional stability.

The thermosetting resin composition includes a thermosetting resin having a benzoxazine ring including a structure (B) represented by formula (2) and a monofunctional or bifunctional phenol compound. In the formula, R1 to R4 are each independently a hydrogen atom or a 1-20C organic group; X is a 1-20C aliphatic or aromatic organic group having a straight chain, branched, or cyclic structure, which may have a hetero element; Y1 and Y2 are each independently a 1-20C organic group which is an aliphatic or aromatic diamine residue having a straight chain, branched, or cyclic structure and may have a hetero element; n and m are each independently an integer of 1-500; and * is a linkage moiety.